Recent experiences in design and construction of high consequence temporary soil nail walls

J. C. W. Toh, M. L. Teoh and G. Mostyn

This paper describes some of the authors’ recent experiences in the design and construction of high consequence temporary soil nail walls.

Various approaches to designing soil nail walls are discussed, including an approach recently adopted by the authors which is considered to be consistent with a limit state design intent.

However, it is reasoned that, regardless of which design approach is adopted, often “construction” aspects are far more significant than “design” aspects in determining how a soil nail wall performs. Three examples are used to demonstrate this point. By “construction” aspects the authors mean effects and deformations resulting from construction activities that are not typically explicitly accounted for in the analysis process, for example deformations from drilling and cleaning holes, vibrations, and small scale / temporary face instability e.g. slumping of interim unsupported excavation faces prior to shotcreting. By “design” aspects the authors mean the deformations of the soil nail wall due to stress relief resulting from progressive excavation of material in front of the wall, i.e. those that can be calculated using analysis.

The paper concludes that a complete soil nail wall design should consider not only the results of the analysis undertaken, but also address issues that may arise related to the construction of the wall, in order to achieve a successful outcome. Some observations and recommendations are made regarding how a design can address these “construction” aspects. It is concluded that the success of a high consequence temporary soil nail wall depends not only on the interaction between the soil and the structural elements, but also their interaction with construction aspects, and therefore a design should seek to address these aspects so far as practical.